Inca Trail permits are now sold out until October 2012. We now have an on-line tool to check availability if you are interested in hiking the Inca Trail to Machu Picchu.
You need 3-4 permits per trekker to cover support staff. Availability of permits can change by the moment, and permits are not guaranteed for a specific date, until the outfitter has presented the money, start date for the Inca Trail, full names, nationality, passport numbers and date of birth to the INC (Instituto de Nacional Cultura), and has confirmed that permits were purchased.
If there are no permits available, there are alternative treks to Machu Picchu that are amazing!